1. Field of the Invention
The present invention relates to a running vehicle having a pair of hydrostatic transmissions, each of which pair includes a hydraulic pump and a hydraulic motor fluidly connected with each other, one of which pair is used for steering and the other is for running-driving, so as to drive and steer the running vehicle by use of a steering operation tool.
2. Related Art
Conventionally, technology where a pair of hydrostatic transmissions (HSTs) are laterally connected, driving axles project laterally from respective HSTs, running-driving wheels are fixed to the outer ends of both axles, wherein movable swash plates as capacity adjusting members for the hydraulic pumps of the HSTs are individually changed in angle thereby driving the left and right running wheels individually, is well-known, as disclosed in, for example, U.S. Pat. No. 4,782,650.
In such constructions, running speeds of the left and right HSTs, when the vehicle is driven straight forward, are equalized, and, when turned, are different.
The above-said running vehicle, however, could not travel straight-forward unless the output rotations of the left and right HSTs completely coincided with each other, adjustments in shipment took much time, and parts and assembly errors had to be diminished so as to improve accuracy. Also, when there was a difference between the capacities of the hydraulic pumps and motors, left or right turning feeling of the vehicle was different, resulting in that the running vehicle was very hard to steer.
Also, the same running vehicle was larger in turning radius due to its lateral arrangement of the pair of HSTs, so that the vehicle had to run in the same place many times for such work as lawn-mowing around trees, thereby deteriorating the working efficiency.
Thus, for overcoming the above problems, a running vehicle including a steering operation tool; a pair of running-driving axles; a pair of running wheels drivingly connected with the pair of running-driving axles; a first differential unit interposed between the pair of running-driving axles; a first hydrostatic transmission for transmitting a driving force to the first differential unit; a pair of steering output shafts; a second differential unit interposed between the pair of steering output shafts; a second hydrostatic transmission for transmitting a driving force to the second differential unit; a first drive train interposed between one of the steering output shafts and one of the running-driving axles, and a second drive train interposed between the other steering output shaft and the other running-driving axle for transmitting the rotating effort to the other running-driving axle in the opposite direction to the first drive train, wherein the second hydrostatic transmission operationally interlocks with the steering operation tool so that the output speed and direction of the second hydraulic transmission is changed by manipulation of the steering operation tool, has come to be invented. The vehicle does not require such labor as above mentioned for precise coincidence between the capacities of the first and second hydrostatic pumps and motors. Also, when both the hydrostatic pumps and motors are arranged in a longitudinal line, the vehicle becomes laterally compact, thereby diminishing the turning radius.
However, it is still desirable to improve the running efficiency of the vehicle when it is driven on a rough road or a soft ground. Also, when such a running vehicle has a plurality of running wheels arranged in a longitudinal direction so as to be made larger in whole length, it is still difficult to diminish the turning radius of the vehicle only by changing the number of rotations of the left and right running-driving wheels.
An object of the present invention is to greatly improve a running efficiency of a running vehicle, when running on a rough road or a soft ground, which includes a steering operation tool; a pair of running-driving axles; a pair of running wheels drivingly connected with the pair of running-driving axles; a first differential unit interposed between the pair of running-driving axles; a first hydrostatic transmission for transmitting a driving force to the first differential unit; a pair of steering output shafts; a second differential unit interposed between the pair of steering output shafts; a second hydrostatic transmission for transmitting a driving force to the second differential unit; a first drive train interposed between one of the steering output shafts and one of the running-driving axles, and a second drive train interposed between the other steering output shaft and the other running-driving axle for transmitting the rotating effort to the other running-driving axle in the opposite direction to the first drive train, wherein the second hydrostatic transmission operationally interlocks with the steering operation tool so that the output speed and direction of the second hydraulic transmission is changed by manipulation of the steering operation tool.
To achieve the object, a pair of running-driven axles are disposed either in front or rear of the pair of running-driving axles, another pair of running wheels are drivingly connected with the pair of running-driven axles, and each of a pair of power transmission mechanisms is interposed between the running-driving axle and the running-driven axle arranged on each common side of the vehicle, so as to rotate the pair of running-driven axles in the same rotational direction of the running-driving axles.
Additionally, in order to further diminish the turning radius of the vehicle, the vehicle may be additionally provided with a pair of steerable running wheels which are steered by manipulation of the steering operation tool.
Another object of the present invention is to further diminish the turning radius of the above-said running vehicle comprising the pair of running-driving axles and wheels, the first and second differential units, the first and second hydrostatic transmissions, the pair of steering output shafts, the first and second drive trains, especially when the vehicle has a plurality of running wheels arranged in a longitudinal direction so as to be made larger in whole length.
To achieve the object, the running-driving wheels are made to be steered by manipulation of the steering operation tool, thereby serving as first steerable running wheels.
In this construction, a pair of second steerable running wheels, which are steered by manipulation of the steering operation tool, are disposed either in front or rear of the pair of first steerable running wheels. The pair of first steerable running wheels are steered either in the same steering direction with or in the opposite steering direction to the second steerable running wheels steered by the manipulation of the steering operation tool. They may be steered selectively either in the same steering direction with or in the opposite steering direction to the second steerable running wheels steered by manipulation of the steering operation tool.
Furthermore, a pair of running-driven axles may be disposed either in front or rear of the pair of running-driving axles, so that the pair of running-driven axles are driven in synchronism with the pair of running-driving axles, and another pair of running wheels may be drivingly connected with the pair of running-driven axles. The running-driven axles may be driven through a pair of power transmission mechanisms, each of which is interposed between the running-driving axle and the running-driven axle arranged on each common side of the vehicle, so as to rotate the pair of running-driven axles in the same rotational direction of said running-driving axles. Alternatively, a third differential unit may be interposed between the pair of running-driven axles, so that the third differential unit receives a driving force taken out from the first hydrostatic transmission. Additionally, the pair of running wheels drivingly connected with the pair of running-driven axles may be steerable so as to be steered by manipulation of the steering operation tool.
Alternatively, in addition to the first steerable running wheels, at least one castor wheel may be disposed either in front or rear of said pair of first steerable running, wheels. Additionally, similar second steerable running wheels or similar running-driven axles may be provided.
These and other objects of the invention will become more apparent in the detailed description and examples which follow.